uboot: (firmwareOdroidC2/C4) don't invoke patch tool, use patches = [] instead

https://github.com/NixOS/nixpkgs/blob/master/pkgs/stdenv/generic/setup.sh#L948
this can do it nicely.

Signed-off-by: Anton Arapov <anton@deadbeef.mx>

nixos/modules/services/misc/nix-optimise.nix

@@ -0,0 +1,57 @@
+{ config, lib, ... }:
+
+with lib;
+
+let
+  cfg = config.nix.optimise;
+in
+
+{
+
+  ###### interface
+
+  options = {
+
+    nix.optimise = {
+
+      automatic = mkOption {
+        default = false;
+        type = types.bool;
+        description = "Automatically run the nix store optimiser at a specific time.";
+      };
+
+      dates = mkOption {
+        default = ["03:45"];
+        type = types.listOf types.str;
+        description = ''
+          Specification (in the format described by
+          <citerefentry><refentrytitle>systemd.time</refentrytitle>
+          <manvolnum>7</manvolnum></citerefentry>) of the time at
+          which the optimiser will run.
+        '';
+      };
+    };
+  };
+
+
+  ###### implementation
+
+  config = {
+    assertions = [
+      {
+        assertion = cfg.automatic -> config.nix.enable;
+        message = ''nix.optimise.automatic requires nix.enable'';
+      }
+    ];
+
+    systemd.services.nix-optimise = lib.mkIf config.nix.enable
+      { description = "Nix Store Optimiser";
+        # No point this if the nix daemon (and thus the nix store) is outside
+        unitConfig.ConditionPathIsReadWrite = "/nix/var/nix/daemon-socket";
+        serviceConfig.ExecStart = "${config.nix.package}/bin/nix-store --optimise";
+        startAt = optionals cfg.automatic cfg.dates;
+      };
+
+  };
+
+}